When running in athletic and other active-wear shoes, very high downward forces are often exerted on the runner's foot which must be cushioned. Such athletic shoes generally have a fairly tough, nonyielding tread made out of a material such as rubber. The conventional solution toward providing cushioning for the foot has been to provide an insole on top of the rubber tread. Such an insole usually distributes cushioning material uniformly on top of the sole, whereas the downward force exerted by the foot on the ground or floor is generally concentrated in the plantar and heel areas of the foot. Insofar as such a uniformly cushioning insole provides a cushioning of relatively hard footfalls, it also continues to cushion the foot after the downward force above the normal gravitational force has been dissipated. This continued overcushioning reduces the "feel" of the foot for the surface. Finally, even where an insole has been provided in conventional constructions, it still may be inadequate to shield the foot from impact due to large downward forces of the foot on the ground or floor.
Previous cushioning techniques have incorporated concentric rings or grooves formed on the bottom of the shoe soles. However, such rings or grooves are independent of one another, and a cushioning effect provided by one ring or groove does not necessarily affect adjacent rings or grooves.
Another problem often encountered in athletic activities is the limited ability of the shoe to resist forward, backward, rightward or leftward shear forces without slipping. In such sports as basketball or tennis, the wearer is often required to quickly change the direction of his motion or to halt altogether. This imposes a large shear force on the sole, which causes the foot to be prone to slipping out from under the wearer. In instances where the sole is successful in continuing to grip the surface, the sudden shear force often causes dislocation, sprain or like injury to the foot, ankle or leg.
A need therefore exists for a sole for an athletic or active-wear shoe which includes means for specifically cushioning the plantar and heel surfaces of the foot against hard footfalls. Further, a need exists for an athletic or activewear shoe with a sole that exhibits enhanced frictional force against shear forces and that at the same time acts to provide a non-slipping, braking, force-absorbing action.